Medial Olfactory Tract Research Articles

The evolutionary trajectories of the individual amygdala nuclei in the common shrew, guinea pig, rabbit, fox and pig: A consequence of embryological fate and mosaic-like evolution.

The amygdala primarily evolved as a danger detector that regulates emotional behaviours and learning. However, it is also engaged in stress responses as well as olfactory/pheromonal and reproductive functions. All of these functions are processed by a set of nuclei which are derived from different telencephalic sources (pallial and subpallial) and have a unique cellular structure and specific connections. It is unclear how these individual anatomical and functional units evolved to fit the amygdala to the specific needs of various mammals. Thus, this study provides quantitative data regarding volumes, neuron density and neuron numbers in the main amygdala nuclei of the common shrew, guinea pig, rabbit, fox and pig - species from across the mammalian phylogeny which differ in brain complexity and ecology. The results show that the volume of the amygdala and its individual nuclei scale with negative allometry relative to brain mass (an allometric coefficient below one). However, in relation to the whole amygdala volume, volumes and volumetric percentages of the lateral (LA) and basomedial (BM) nuclei scale with positive allometry, for the medial (ME) and lateral olfactory tract (NLOT) nuclei these parameters scale with negative allometry while the values of these parameters for the basolateral (BL), central (CE) and cortical (CO) nuclei scale with isometry. Moreover, density of neurons scales with strong negative allometry relative to both brain mass and amygdala volume with values of allometric coefficient below zero across studied species. This value for BL is significantly lower than that for the whole amygdala, for ME it is significantly higher while values for NLOT, CE, CO, LA and BM are quite similar to the value for whole amygdala. Finally, neuron numbers in the whole amygdala and its individual nuclei scale with negative allometry in relation to brain mass. However, in relation to the number of neurons in the whole amygdala, neuron numbers and percentages of neurons for LA and BM scale with positive allometry, for BL and NLOT they scale with negative allometry while the values of these parameters for CE, CO and ME scale with isometry. In conclusion, all of these results indicate that each of the nuclei studied displays a different and unique pattern of evolution in relation to brain mass or the whole amygdala volume. These patterns do not match with the various classical concepts of amygdala parcellation; however, in some way, they reflect diversity revealed by the expression of homeobox genes in various embryological studies.

Olfactory bulb SARS-CoV-2 infection is not paralleled by the presence of virus in other central nervous system areas.

Olfactory bulb SARS-CoV-2 infection is not paralleled by the presence of virus in other central nervous system areas.

Alpha-melanocyte stimulating hormone immunoreactivity in the brain of the cichlid fish Oreochromis mossambicus

This study reports the distribution of a pro-opiomelanocortin-derived neuropeptide α–MSH in the brain of the cichlid fish Oreochromis mossambicus. α–MSH-ir fibres were found in the granule cell layer of the olfactory bulb, the medial olfactory tract, the pallium and the subpallium, whereas in the preoptic area of the telencephalon, few large α–MSH-ir perikarya along with extensively labeled fibres were observed close to the ventricular border. Dense network of α–MSH-ir fibres were seen in the hypothalamic areas such as the nucleus preopticus pars magnocellularis, the nucleus preopticus pars parvocellularis, the suprachiasmatic nucleus, the nucleus anterior tuberis, the paraventricular organ, the subdivisions of the nucleus recessus lateralis and the nucleus recessus posterioris. In the nucleus lateralis pars medialis, some α–MSH-ir perikarya and fibres were found along the ventricular margin. In the diencephalon, numerous α–MSH-ir fibres were detected in the nucleus posterior tuberis, the nucleus of the fasciculus longitudinalis medialis and the nucleus preglomerulosus medialis, whereas in the mesencephalon, α–MSH-ir fibres were located in the optic tectum, the torus semicircularis and the tegmentum. In the rhombencephalon, α–MSH-ir fibres were confined to the medial octavolateralis nucleus and the descending octaval nucleus. In the pituitary gland, densely packed α–MSH-ir cells were observed in the pars intermedia region. The widespread distribution of α–MSH-immunoreactivity throughout the brain and the pituitary gland suggests a role for α–MSH peptide in regulation of several neuroendocrine and sensorimotor functions as well as darkening of pigmentation in the tilapia.

Systematization and Description of Arterial Vascularization of the Paleopallia Area on the Brain Surface of Chinchilla (Chinchilla lanigera)

Background: Chinchilla (Chinchilla lanigera) is a small rodent that in recent years has been increasingly used as a laboratory animal by different researchers. Brain irrigation is the object of study by several authors, being chinchilla classified as a vertebrobasillary animal, that is, it does not depend on the internal carotid artery to originate its cerebral arterial vascularization. Thus, the objective of this study was to systematize and describe the branches of the rostral, middle and caudal cerebral arteries that vascularized the paleopallia area of the chinchilla. Materials, Methods & Results: Thirty Chinchilla lanigera brains were used in this study, 17 females and 13 adult males from farms in the municipalities of Viamão and Santa Maria in the state of Rio Grande do Sul, Brazil. The animals were heparinized, with 5000 IU / animal, and after 30 min were sacrificed with 8 mL / 2.5% sodium thiopental animal, both intraperitoneally. The thoracic cavity was opened, the cardiac apex sectioned and the aortic arch was cannulated through the left ventricle. The arterial system was flushed with 0.9% cooled saline, 100mL / animal and then filled with 603 latex stained red with specific dye. The skin was recessed and a bone window opened in the cranial vault. Thus the pieces were fixed in 20% formaldehyde for seven days and after this period, the brain with a cervical spinal cord segment was removed and ventral schematic drawings of all preparations were prepared. The Veterinary Anatomical Nomina (2017) was used to name the cerebral arteries and their branches and for the statistical analysis of the results, the percentage calculation was applied. Brain irrigation in the chinchilla was supplied by the basilar artery, which was formed by anastomosis of the terminal branches of the right and left vertebral arteries, in the most caudal portion of the oblong medulla. The paleopallia areas corresponded to the olfactory trine, lateral brain fossa, piriform lobe, bulb and olfactory peduncle, and the medial and lateral olfactory tracts. Irrigation of the chinchilla paleopallia area was supplied by central branches from the caudal, middle and rostral cerebral arteries, and by the central branches originating from the terminal branches of the basilar artery.Discussion: Justifying the discussion about the systematization and description of arterial vascularization of the paleopallia area of the chinchilla brain, it was compared to other species such as wild boar, nutria, rabbit and greasy of the field, because only in these animals were found references on the subject. . The central branches of the cerebral arteries were mainly responsible for the irrigation of the paleopallia areas of the chinchilla brain, as well as in the species already mentioned. Due to the variation of the types of arterial vascularization in each of these species, small differences were observed, and these central vessels may also be emitted from the rostral branch of the internal carotid artery, such as in the rabbit and fatty grapefruit, or from the brain carotid artery as in wildboar. Similarities between chinchilla and nutria were also observed, and these central branches may originate from the terminal branches of the basilar artery in both species.

Leucine-enkephalin-immunoreactive neurons in the brain of the cichlid fish Oreochromis mossambicus

Enkephalins are the pentapeptides involved in pain relief and neuroendocrine responses with high affinity for delta opioid receptors in vertebrates. In the present investigation, we studied the distribution of leucine-enkephalin-immunoreactive (L-ENK-ir) neurons in the brain of the cichlid fish Oreochromis mossambicus. Application of the antisera against L-ENK revealed the presence of numerous L-ENK-ir perikarya and fibres in subdivisions of the dorsal and the ventral telencephalon, the medial olfactory tract and the nucleus entopeduncularis, whereas intensely labelled L-ENK-ir fibres were noticed in the olfactory bulb. Furthermore, the presence of L-ENK-ir cells and dense accumulations of fibres in the preoptic area and its subdivisions, the nucleus preopticus pars magnocellularis and the nucleus preopticus pars parvocellularis suggested a role for this peptide in regulation of reproduction. While intensely labelled cells and fibres were found in the nucleus lateralis tuberis pars lateralis as well as the nucleus lateralis tuberis pars medialis, some L-ENK-ir fibres were seen at the hypothalamo-hypophyseal tract indicating the possible hypophysiotrophic role for this peptide. Numerous L-ENK-ir cells and dense network of fibres were observed in the subdivisions of the nucleus recess lateralis and the pretectal area, whereas intensely labelled thick network of L-ENK- fibres were found in the ventromedial thalamic nucleus, the sub-layers of the optic tectum and the rostral spinal cord. The widespread distribution of L-ENK-immunoreactivity in the olfactory bulb, the telencephalon, the diencephalon and the mesencephalon regions of the brain as well as the spinal cord suggests the possible involvement of this peptide in the regulation of diverse functions such as neuroendocrine, antinociceptive, visual and olfactory responses in O. mossambicus.

Systematization and Description of the Arterial Blood Supply of the Paleopallia areas in the Brain Surface of the Wild Boar (Sus scrofa scrofa)

Background: The study was performed on wild boar (Sus scrofa scrofa) wich is a wild ancestor of the domestic pig and is not part of Brazilian fauna. The arterial blood supply of the encephalus has been studied by some researchers, who have systematized the cerebral blood supply from the rostral and caudal epidural rete mirabile and its sources in wild boar until the blood supply of the base of the brain. The objective was to improve the understanding of the arterial blood supply of the brain, particularly the paleopallium, of the wild boar and to provide a reference for comparative anatomy studies. Materials, Methods & Results: A total of 30 brains were obtained from an officially authorised slaughterhouse and approved by Brazilian Institute of Environment and Natural Renowable Resources. The animals were desensitized, followed by bleending of the jugular veins and common carotid arteries near the entrance of the thorax, according to the slaughter procedure. Finally, the animals were decapitated at the level of axis vertebra. The cerebral arterial system of each animal was rinsed (cooled saline containing 2500 IU of heparin) and drained by the jugular veins, and vessels were filled with latex 603 stained with specific red dye. The heads were submerged for one hour in running water immersed in 20% formaldehyde for fixation; the brains were removed along with a cervical segment of the spinal cord. The duramater was removed, and the arteries were dissected. Schematic drawings of the ventral view of the all preparations were made using magnifying glasses and photographic records. The Nomina Anatomica Veterinaria was used to named the cerebral arteries and their branches, and calculation of pecentages was applied in the statistical analysis. The cerebral carotid artery originating from the rostral epidural rete mirabile emitted a rostral branch and a caudal branch on the side of the hypophysis gland. The rostral branch emitted one to three middle cerebral arteries and continued as rostral cerebral artery. The latter emitted the superficial and perforating central arteries, lateral rhinal artery, ethmoidal artery, medial branch and medial rhinal artery. Discussion: Wild boar is a macrosmatic animal, it presents well-developed areas of the paleopallium that are exclusively olfactory. Its extensive paleopallium was nourished by branches of the rostral cerebral artery and its collateral branches, including the lateral rhinal, ethmoidal, and medial branch and the medial rhinal artery. The rostral cerebral arteries and their collateral branches supplied blood to the olfactory bulb, olfactory peduncle, two-thirds of the lateral olfactory tract, medial olfactory tract, and rostral two-thirds of the olfactory trigone. The medial cerebral arteries within the lateral fossa of the brain, emitted superficial rostral central branches to the paleopallium, perforating central branches (striated) to the lateral fossa of the brain and caudal third of the olfactory trigone and caudal central branches to the piriform lobe. The rostral most two-thirds of a small medial band of the piriform lobe was vascularised by central branches originating mainly from the rostral branch of the cerebral cartotid artery. The paleopallium in the wild boar was nourished by branches of the cerebral rostral, middle and caudal arteries and by the central branches of the cerebral carotid artery. The arterial blood supply of the paleopallium in the wild boar was compared to the chinchilla, nutria, rabbit and pampas fox. Three cerebral vessels were mainly responsable for the emission of the central branches that supplied blood to the paleopallium, namely the middle, rostral, and caudal cerebral arteries. The differences or variations among these species were due to the type of cerebral blood supply in the formation of the cerebral arterial circle.Keywords : anatomy, brain, paleopallia, arteries, Artiodactila, wild boar.

Distribution of tyrosine hydroxylase-immunoreactive neurons in the brain of the viviparous fish Gambusia affinis

Tyrosine hydroxylase (TH) is the common precursor enzyme involved in the biosynthetic pathway of the catecholaminergic neurotransmitters, dopamine and norepinephrine. In this investigation, the neuroanatomical distribution of TH-immunoreactivity was studied in the brain of the female mosquitofish Gambusia affinis. Numerous intensely stained TH-immunoreactive (ir) neurons were scattered in the olfactory bulb with their fibres extending towards the medial olfactory tract, whereas few telencephalic TH-ir cells with distinct fibres were observed in the dorsal nucleus of area ventralis telencephali and the posterior nucleus of area ventralis telencephali regions. Large TH-ir cell populations were seen in the suprachiasmatic nucleus and the nucleus dorsomedialis thalami regions of the diencephalon. Distinct TH-ir cells with long fibres were found at the preoptic area and the nucleus preopticus pars magnocellularis as well as the nucleus preopticus pars parvocellularis regions. Numerous intensely stained TH-ir cells were observed in the paraventricular organ and the nucleus posterior tuberis regions, whereas moderately stained cells were present in the nucleus of recessus lateralis medialis. Several TH-ir neurons were detected in medial and lateral subdivisions of the nucleus lateralis tuberis. Furthermore, the projections of the TH-ir fibres were seen in the proximal pars distalis region of the pituitary gland, where gonadotropin-secreting cells are located, suggesting the communication between TH cells and gonadotrope cells. In the rostral spinal cord, dense aggregations of the TH-ir fibres were noticed. Overall, the widespread distribution of the TH-ir neurons throughout the brain and their fibres in the spinal cord and the pituitary gland suggests diverse roles for the catecholaminergic neurons in various physiological functions including reproduction in the mosquitofish.

Distribution of endomorphin-like-immunoreactive neurones in the brain of the cichlid fish Oreochromis mossambicus.

Endomorphins (EMs) are tetrapeptides involved in pain and neuroendocrine responses with a high affinity for μ-opioid receptors in mammals. In the present study, we investigated the distribution of EM-like-immunoreactive (EM-L-IR) neurones in the brain of the cichlid fish Oreochromis mossambicus. Application of antisera against EM-1 and 2 (EM-1-2) revealed the presence of EM-L-IR somata and fibres throughout the different subdivisions of the olfactory bulb, such as the olfactory nerve layer and the granule cell layer. Although the extensions of EM-L-IR fibres were seen along the medial olfactory tract, intensely labelled EM-L-IR somata were found in different subdivisions of the telencephalon. In the diencephalon, intensely stained EM-L-IR neurones were noted in the preoptic area, the nucleus preopticus pars magnocellularis, the suprachiasmatic nucleus, the nucleus lateralis tuberis pars lateralis and the nucleus lateralis tuberis pars medialis regions, whereas projections of EM-L-IR fibres were also seen along the hypothalamic-hypophyseal tract, suggesting a possible hypophysiotrophic role for these neurones. Intense to moderately stained EM-L-IR neurones were noted in different subdivisions of thalamic nucleus, such as the dorsal posterior thalamic nucleus, commissura posterior, ventromedial thalamic nucleus, nucleus posterior tuberis, ventrolateral thalamic nucleus and medial preglomerular nucleus. Numerous intensely stained perikarya and axonal fibres were also noted throughout the inferior lobe, along the periventricular margin of the reccessus lateralis and in the nucleus recesus lateralis regions. In addition, numerous moderately labelled EM-like neuronal populations were found in the secondary gustatory nucleus and rostral spinal cord. The widespread distribution of EM-L-IR neurones throughout the brain and spinal cord indicates the diverse roles for these cells in neuroendocrine and neuromodulatory responses for the first time in fish. The present study provides further insights into the possible existence of EM-like peptides in early vertebrate lines and suggests that these peptides might have been well-conserved during the course of evolution.

Electrophysiological characterization of male goldfish (Carassius auratus) ventral preoptic area neurons receiving olfactory inputs.

Chemical communication via sex pheromones is critical for successful reproduction but the underlying neural mechanisms are not well-understood. The goldfish is a tractable model because sex pheromones have been well-characterized in this species. We used male goldfish forebrain explants in vitro and performed whole-cell current clamp recordings from single neurons in the ventral preoptic area (vPOA) to characterize their membrane properties and synaptic inputs from the olfactory bulbs (OB). Principle component and cluster analyses based on intrinsic membrane properties of vPOA neurons (N = 107) revealed five (I–V) distinct cell groups. These cells displayed differences in their input resistance (Rinput: I < II < IV < III = V), time constant (TC: I = II < IV < III = V), and threshold current (Ithreshold: I > II = IV > III = V). Evidence from electrical stimulation of the OB and application of receptor antagonists suggests that vPOA neurons receive monosynaptic glutamatergic inputs via the medial olfactory tract, with connectivity varying among neuronal groups [I (24%), II (40%), III (0%), IV (34%), and V (2%)].

Calcium binding protein calretinin (29 kD) localization in the forebrain of the cichlid fish: An immunohistochemical study

Ionic regulation is essential for the metabolism and cellular function. For many physiological processes, ionic calcium (Ca+2) is important for example muscle contractions, nerve signaling, membrane permeability, cell division and hormone release. In nerve cells, the excess intracellular concentration of Ca+2 causes cell death. It has been shown that certain calcium binding proteins (CaBPs) are essential for Ca+2 homeostasis and protect neurons from excess Ca+2 influx.We are for the first time showing an unusual calretinin (CR) expression and significant differences in its occurrence in the forebrain of the cichlid fish (Cynotilapia sp.) compared to other teleosts. CR labeled neurons were seen in the dorsal and lateral part of the dorsal telencephalic area, entopeduncular nucleus (EN), nucleus preopticus (NPO), diffuse nucleus of lateral torus (NDTL), ventral hypothalamic nucleus (VH), preglomerular nucleus (NPG) and optic tectum. Surprisingly, large numbers of CR immunoreactive perikarya were noted in the optic chiasma (Oc). These neurons were oval with elongated processes and forming a huge fiber network in the Oc. Enormously CR stained fibers were seen in the lateral and medial olfactory tract. Widespread distributions of strongly CR labeled fibers were observed around the EN projecting dorsally into the telencephalon, Oc and optic nerve. Presence of CR in the NPO suggests that it may be involved in the hormonal regulation by the pituitary. As in vertebrates EN plays an important role in sensory functions, massive localization CR in the EN may suggests role of CR in sensory functions of the cichlid fish.

Gender-typical olfactory regulation of sexual behavior in goldfish.

It is known that olfaction is essential for the occurrence of sexual behavior in male goldfish. Sex pheromones from ovulatory females elicit male sexual behavior, chasing, and sperm releasing act. In female goldfish, ovarian prostaglandin F2α (PGF) elicits female sexual behavior, egg releasing act. It has been considered that olfaction does not affect sexual behavior in female goldfish. In the present study, we re-examined the involvement of olfaction in sexual behavior of female goldfish. Olfaction was blocked in male and female goldfish by two methods: nasal occlusion (NO) which blocks the reception of olfactants, and olfactory tract section (OTX) which blocks transmission of olfactory information from the olfactory bulb to the telencephalon. Sexual behavior of goldfish was induced by administration of PGF to females, an established method for inducing goldfish sexual behavior in both sexes. Sexual behavior in males was suppressed by NO and OTX as previously reported because of lack of pheromone stimulation. In females, NO suppressed sexual behavior but OTX did not affect the occurrence of sexual behavior. Females treated with both NO and OTX performed sexual behavior normally. These results indicate that olfaction is essential in female goldfish to perform sexual behavior as in males but in a different manner. The lack of olfaction in males causes lack of pheromonal stimulation, resulting in no behavior elicited. Whereas the results of female experiments suggest that lack of olfaction in females causes strong inhibition of sexual behavior mediated by the olfactory pathway. Olfactory tract section is considered to block the pathway and remove this inhibition, resulting in the resumption of the behavior. By subtract sectioning of the olfactory tract, it was found that this inhibition was mediated by the medial olfactory tracts, not the lateral olfactory tracts. Thus, it is concluded that goldfish has gender-typical olfactory regulation for sexual behavior.

Medial and lateral perforant path evoked potentials are selectively modulated by pairing with glutamatergic activation of locus coeruleus in the dentate gyrus of the anesthetized rat

Norepinephrine (NE) in vitro produces long-lasting potentiation of medial perforant path input and depression of lateral perforant path input to dentate gyrus in the rat. Similar, but highly transient, effects have been reported in vivo using paragigantocellular stimulation to release NE. The present study uses alternate stimulation of the medial perforant path and lateral olfactory tract (eliciting a lateral perforant path-evoked potential) to examine the effects of glutamatergic activation of locus coeruleus (LC) on the two pathways for up to 3 h post-LC activation. In the first experiment, the expected potentiation of the medial perforant path population spike in dentate gyrus was observed, but without accompanying depression of the lateral perforant path-mediated evoked potential (lateral olfactory tract stimulation, 60 s ISI). In a second experiment, with more frequent pairing of input with NE release (10 s ISI), significant potentiation of lateral perforant path-mediated input to dentate gyrus occurred, but potentiation of medial perforant path input was not seen. A third experiment with a 30 s ISI again produced potentiation of lateral perforant path-mediated input without potentiation of the medial perforant path population spike. The size of effects with the 30 s ISI was intermediate between that seen with 10 s and 60 s ISI. Potentiation of lateral perforant path over medial perforant path input has previously been reported with acute nicotinic activation of the LC. This outcome also resembles heterosynaptic modulation previously reported with tetanic potentiation. The data argue for a competitive relationship between medial and lateral perforant path inputs to dentate gyrus and suggest pairing with increased NE produces a bias favoring one or the other pathway depending on parameters such as strength and frequency. NE potentiating effects on lateral perforant path input here may also have occurred in entorhinal cortex (EC) given the system-wide NE release with LC activation.

Cladistic Analysis of Olfactory and Vomeronasal Systems

Most tetrapods possess two nasal organs for detecting chemicals in their environment, which are the sensory detectors of the olfactory and vomeronasal systems. The seventies’ view that the olfactory system was only devoted to sense volatiles, whereas the vomeronasal system was exclusively specialized for pheromone detection was challenged by accumulating data showing deep anatomical and functional interrelationships between both systems. In addition, the assumption that the vomeronasal system appeared as an adaptation to terrestrial life is being questioned as well. The aim of the present work is to use a comparative strategy to gain insight in our understanding of the evolution of chemical “cortex.” We have analyzed the organization of the olfactory and vomeronasal cortices of reptiles, marsupials, and placental mammals and we have compared our findings with data from other taxa in order to better understand the evolutionary history of the nasal sensory systems in vertebrates. The olfactory and vomeronsasal cortices have been re-investigated in garter snakes (Thamnophis sirtalis), short-tailed opossums (Monodelphis domestica), and rats (Rattus norvegicus) by tracing the efferents of the main and accessory olfactory bulbs using injections of neuroanatomical anterograde tracers (dextran-amines). In snakes, the medial olfactory tract is quite evident, whereas the main vomeronasal-recipient structure, the nucleus sphaericus is a folded cortical-like structure, located at the caudal edge of the amygdala. In marsupials, which are acallosal mammals, the rhinal fissure is relatively dorsal and the olfactory and vomeronasal cortices relatively expanded. Placental mammals, like marsupials, show partially overlapping olfactory and vomeronasal projections in the rostral basal telencephalon. These data raise the interesting question of how the telencephalon has been re-organized in different groups according to the biological relevance of chemical senses.

Differential bulbar and extrabulbar projections of diverse olfactory receptor neuron populations in the adult zebrafish (Danio rerio)

Immunohistochemical methods were used to characterize the expression of two calcium-binding proteins, calretinin (CR) and S100, in the olfactory rosette of the adult zebrafish. These proteins are expressed in different sets of sensory neurons, and together represent a large proportion of these cells. Double immunofluorescence for CR and Gα(olf) protein, and CR immunoelectron microscopy, indicated that most CR-immunoreactive (ir) cells were ciliary neurons. Differential S100- and CR-ir projections to glomerular fields of the olfactory bulb were also observed, although these projections overlap in some glomeruli. Application of the carbocyanine dye DiI to either S100-ir or CR-ir glomerular regions led to labeling of cells mostly similar to S100-ir and CR-ir neurons, respectively. Instead, these bulbar regions project to similar telencephalic targets. On the other hand, antibodies against keyhole limpet hemocyanin (KLH)-stained numerous sensory cells in the olfactory rosette, including cells that were CR- and S100-negative. This antiserum also stained most primary bulbar projections and revealed extrabulbar olfactory primary projections coursing to the ventral area of the telencephalon through the medial olfactory tract. This extrabulbar projection was confirmed by tract-tracing with DiI. A loose association of this extrabulbar primary olfactory projection and the catecholaminergic populations of the ventral area was also observed with double tyrosine hydroxylase/KLH-like immunohistochemistry. Comparison between KLH-like-ir pathways and the structures revealed by FMRFamide immunohistochemistry (a marker of terminal ganglion cells and fibers) indicated that the KLH-like-ir extrabulbar projection was different from the terminal nerve system. The significance of the extrabulbar olfactory projection of zebrafish is discussed.

Neuromodulatory Effect of GnRH on the Synaptic Transmission of the Olfactory Bulbar Neural Circuit in Goldfish, Carassius auratus

Gonadotropin-releasing hormone (GnRH) is well known as a hypophysiotropic hormone that is produced in the hypothalamus and facilitates the release of gonadotropins from the pituitary gonadotropes. On the other hand, the functions of extrahypothalamic GnRH systems still remain elusive. Here we examined whether the activity of the olfactory bulbar neural circuits is modulated by GnRH that originates mainly from the terminal nerve (TN) GnRH system in goldfish (Carassius auratus). As the morphological basis, we first observed that goldfish TNs mainly express salmon GnRH (sGnRH) mRNA and that sGnRH-immunoreactive fibers are distributed in both the mitral and the granule cell layers. We then examined by extracellular recordings the effect of GnRH on the electrically evoked in vitro field potentials that arise from synaptic activities from mitral to granule cells. We found that GnRH enhances the amplitude of the field potentials. Furthermore, these effects were observed in both cases when the field potentials were evoked by stimulating either the lateral or the medial olfactory tract, conveying functionally different sensory information, separately, and suggesting that GnRH may modulate the responsiveness to wide categories of odorants in the olfactory bulb. Because GnRH also changed the paired-pulse ratio, it is suggested that the increased amplitude of the field potential results from changes in the presynaptic glutamate release of mitral cells rather than the increase in the glutamate receptor sensitivity of granule cells. These results suggest that TN regulates the olfactory responsiveness of animals appropriately by releasing sGnRH peptides in the olfactory bulbar neural circuits.

Reproductive phase‐related variations in cocaine‐ and amphetamine‐regulated transcript (CART) in the olfactory system, forebrain, and pituitary of the female catfish, Clarias batrachus (Linn.)

The annual sexual cycle of Clarias batrachus is divisible into resting (December-January), preparatory (February-April), prespawning (May-June), spawning (July- August), and postspawning (September-November) phases. The gonosomatic indices rose steadily through the preparatory and prespawning phases, peaked in the spawning phase, and were greatly reduced during the postspawning and resting phases. A clear pattern of change was also identified in the immunocytochemical profile of the luteinizing hormone (LH) cells in the pituitary. These changes were correlated with the cocaine- and amphetamine-regulated transcript (CART)-immunoreactive system in the forebrain and pituitary. In the olfactory bulb, CART immunoreactivity in the terminal fields of the mitral cell layer, granule cells, and medial olfactory tracts gradually decreased during the resting through prespawning phases. However, it was considerably augmented during spawning (P < 0.001) and showed highest activity in the postspawning phase (P < 0.001). A different pattern was noticed in the fibers and/or neurons of the lateral part of ventral telencephalic area, the entopeduncular nucleus, and the dorsal part of the nucleus preopticus periventricularis. In these areas, intense immunoreactivity seen in preparatory phase, declined during prespawning (P < 0.01) then through spawning, and was partially augmented during the postspawning and resting phases (P < 0.05). A similar pattern was also seen in the nucleus preglomerulosus lateralis and medialis, nucleus dorsalis posterioris of thalamus, lobobulbar nucleus, and the nucleus of posterior recess. CART was transiently expressed in LH cells in the pituitary during the preparatory period. We suggest that the CART system may play a role in triggering the brain-pituitary-ovary axis at the onset of the preparatory phase.

Role of olfaction and vision cues in feeding behavior and alarm reaction in the catfish pintado, Pseudoplatystoma corruscans

Experiments were performed to investigate senses that are essential for mediating fright reaction and food behavior in Pseudoplatystoma corruscans, pintado. The dilemma “to feed or to flee” was also analyzed in fishes with intact and sectioned olfactory tracts, stimulated by alarm substance extracts and food. Fishes were arranged into five groups: fish with intact lateral olfactory tracts (LOT), fish with intact medial olfactory tract (MOT), fish with tracts totally sectioned (TOTAL, both LOT and MOT), sham operated, and nonoperated fish. The five groups were submitted to either alarm substance extract and food stimulus or to distilled water (control) and food stimulus. Fish reacted to food independently of which tract (LOT, MOT or TOTAL) was sectioned; vision seems necessary and elemental to detect and deflagrate food response. Latency of the responses to each reaction was different between groups. None of the fish with sectioned tracts reacted to alarm substance extract, while sham- and nonoperated fish showed the typical alarm behavior response, leading to the conclusion that olfaction is essential for mediating alarm response. These results indicate that others sense systems (e.g., vision) are sufficient to trigger and elicit feeding behavior and that olfaction is not necessary to fully maintain food detection to qualitative and quantitative extent. However, olfactory tract integrity seems to be required for mediation of alarm reaction in P. corruscans.

Neuronal nitric oxide synthase in the olfactory system, forebrain, pituitary and retina of the adult teleost Clarias batrachus

Immunocytochemical application of antibodies against nNOS to the brain sections of Clarias batrachus revealed intense immunoreactivity in several olfactory receptor neurons (ORNs), in their axons over the olfactory nerve, and terminals in the olfactory glomeruli. Several basal cells in the olfactory epithelium showed NOS immunoreactivity. Application of post-embedding immunoelectron microscopy showed nNOS labeled gold particles in apical cilia, dendrites and soma of the ORNs and also in the axon terminals in the glomeruli of the olfactory bulb. nNOS containing fibers were also encountered in the medial olfactory tracts (MOTs). Bilateral ablation of the olfactory organ resulted in total loss of nNOS immunoreactivity in the fascicles of the olfactory nerve layer and also in the MOT. nNOS immunoreactivity was seen in several cells of the nucleus preopticus (NPO) and their axons that innervate the pituitary gland. Some cells in the floor of the tuberal area were stained positive with nNOS antibodies. nNOS immunolabeled cells were seen in all the three components of the pituitary gland with light as well as post-embedding immunoelectron microscopy. While several nNOS immunoreactive fibers were seen in rostral pars distalis, a much limited fiber population was seen in the proximal pars distalis. In addition, conspicuous immunoreactivity was noticed in some ganglion cells in the retina and in some fibers of the optic nerve traceable to the optic tectum. The NO containing system in this fish appears to be similar to that in other fishes.

Association of cocaine- and amphetamine-regulated transcript and neuropeptide Y in the forebrain and pituitary of the catfish, Clarias batrachus: A double immunofluorescent labeling study

Cocaine- and amphetamine-regulated transcript (CART) and neuropeptide Y (NPY) are involved in the regulation of food intake, body weight, pituitary hormones, and reproduction. While CART and NPY occupy overlapping fields in the brain of mammals, little is known about the interaction between these peptide-containing systems in other vertebrates. We explored neuroanatomical associations between CART and NPY in the olfactory system, forebrain and pituitary of the catfish, Clarias batrachus, using double immunofluorescence method. NPY-containing fascicles from olfactory receptor neurons innervated the olfactory glomeruli and mitral cell layer in close association with CART-containing terminal fields. Distinct CART- or NPY-containing fibers were seen in the medial olfactory tract. In the dorsal telencephalon, CART- and NPY-immunoreactive axons were closely associated in area dorsalis telencephali/pars lateralis dorsalis (Dld), and posterioris (Dlp). In the ventral telencephalon, while most of the cells of nucleus entopeduncularis (NE) showed the presence of CART as well as NPY, a few cells with only NPY-immunoreactivity were observed. Similarly, a CART and NPY colocalized cell population was prominent in the preoptic area (POA); and a small population of cells with NPY-immunoreactivity was also evident. Other areas where CART and NPY were colocalized included fibers in the tuberal area, inferior lobe, neurohypophysis, proximal pars distalis and pars intermedia of the pituitary. No association between CART and NPY was observed in the thalamus and habenular ganglion. These results suggest that CART- and NPY-peptidergic systems may interact in NE, POA, tuberal area, certain telencephalic areas and pituitary and jointly process information relating to reproduction, feeding and neuroendocrine regulation.

Reproduction phase‐related variations in neuropeptide Y immunoreactivity in the olfactory system, forebrain, and pituitary of the female catfish, Clarias batrachus (Linn.)

The aim of this study was to determine whether neuropeptide Y (NPY) immunoreactivity in the cells and fibers in the forebrain and pituitary of Clarias batrachus is linked to the annual reproductive cycle. A steady rise in luteinizing hormone (LH) immunoreactivity was seen in the pituitary through preparatory (February-April) and prespawning (May-June) phases; it was greatly reduced during spawning (July-August; P < 0.001) and partially replenished during postspawning (September-November; P < 0.01) through resting (December-January) phases. Although NPY immunoreactivity in olfactory receptor neurons and olfactory nerve layer in olfactory bulb was gradually augmented during resting through prespawning phases (P < 0.001), attaining a peak in spawning phase (P < 0.001), a dramatic decline was encountered during postspawning phase (P < 0.001). A similar pattern was also observed in NPY-containing fibers of the medial olfactory tract (MOT) and pituitary. However, a different pattern of NPY immunoreactivity was observed in the neurons of nucleus entopeduncularis (NE) and nucleus preopticus periventricularis (NPP). Whereas these neurons and fibers in the forebrain showed significant augmentation during the resting through prespawning phases (P < 0.001), the immunoreactivity dramatically declined during spawning (P < 0.001) and was partially replenished in the postspawning phase. Testosterone injection of juveniles significantly augmented (P < 0.001) NPY immunoreactivity in NE neurons. We suggest that NPY cells of NE and NPP, and related fiber systems, might be involved in processing of sex steroid-borne information and regulation of the gonadotropin-releasing hormone-LH axis.